Electronic and kinetic isotope effects on the electrooxidation of benzyl alcohols by a monoxo ruthenium (V) complex of tetramethylcyclam

Abstract

The electrooxidation of substituted benzyl alcohols by trans-[Ru v(TMC)(O)(NCO)] 2+ (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) was studied in acetonitrile by rotating disc voltammetry. The second order rate constant between Ru VO and the benzyl alcohols increases in the presence of electron donating substituents and decreases in the presence of electron withdrawing groups. A linear Hammett plot with a slope of −2.0 was obtained. The large negative reaction constant is consistent with a build up of positive charge at the alcohol in the transition state. The primary kinetic isotope effect ( k H/ k D) in benzy] alcohol oxidation was determined to be 4.1. The results are consistent with a mechanism involving hydrogen atom abstraction by the oxo ligand on the ruthenium complex.